In a known method for controlling a cooking process in a cooking appliance including a cooking chamber, on or in which a heating source is provided for heating the cooking chamber, and further including a sensor for measuring a gas concentration in the cooking chamber as well as an electric or electronic control system which contains an evaluation circuit and a memory and is in signal communication with the sensor, initially, a cooking end value stored in the memory is ascertained by the evaluation circuit as a function of a food to be cooked, which is manually selected or automatically identified. As soon as the value of a variable depending on the output signal of the sensor falls below the cooking end value after the beginning of the cooking process, a cooking appliance function is automatically triggered. Thus, in the known method, the cooking appliance function, for example, switching off the heating source, is automatically triggered when the gas concentration of a gas escaping from the food to be cooked during the cooking process falls below a predetermined cooking end value.
The cooking end values for individual foods to be cooked were previously determined by tests. During the operation of conventional cooking appliances, ambient air is passed through the cooking chamber thereof. In the process, a fan located in the cooking appliance draws in ambient air through air inlet openings and exhausts vapors from the cooking chamber through a vapor duct. In this connection, the volume of ambient air drawn through the cooking chamber is always significantly larger than the volume of gases released by the food to be cooked during the cooking process. Therefore, the sensor detects an instantaneous gas concentration since the gases produced by the cooking process are continuously exhausted by the fan and thus removed from the cooking chamber. These gases do not concentrate in the cooking chamber.
The known method has the disadvantage that the cooking end value is dependent on the quantity of food to be cooked and on its distribution in the cooking chamber, for example, due to the use of different baking or roasting pans. Therefore, different cooking end values are obtained even for one and the same recipe. This leads to a multitude of cooking end values so that either complex control is required to detect the quantity and distribution of the food to be cooked, or the user must make further entries, which reduces the ease-of-use.
Moreover, a further method for controlling a cooking process in the form of a bread-baking process is known from German Patent Application D method only relates to bread-baking processes, it is not necessary here to identify the type of food to be cooked. In the known bread-baking method, the bread-baking process is controlled via the variation of the gas density with time in the cooking chamber, which is measured using a gas sensor. Here, for example, the heating element and the fan are automatically switched off, and the bread-baking process is thereby terminated, as soon as the gas density has fallen below a maximum value by a predetermined amount. Alternatively, it is proposed to use the change in gradient of the gas density, i.e., the change in the first derivative of the gas density with respect to time, for controlling the bread-baking process after the maximum value of the gas density has been detected by the gas sensor.
Another method is known from European Patent Application EP 0 455 169 A2. In this method, electrical output voltages present at a gas sensor are processed in an evaluation of a control system when two predetermined temperatures are reached. In the process, the gas sensor transmits to the evaluation circuit a first output voltage before the beginning of the cooking process, i.e., at the initial temperature for the cooking process, and a second output voltage when a predetermined temperature is reached during the cooking process; a cooking quotient being calculated from the two output voltages of the gas sensor. This cooking quotient is compared with predetermined reference values stored in a memory. The type of food to be cooked is inferred depending on whether the cooking quotient is greater or less than a first or a second reference value. For example, if the cooking quotient falls below the second reference value, the cooking process is continued for a predetermined time at a further predetermined cooking temperature, and automatically terminated at a later point in time.